Daily Climate: Three sets of scientists in the same week have helped narrow the uncertainties about how the natural world will respond to extra carbon dioxide in the atmosphere caused by the burning of fossil fuels. Carbon locked in the frozen earth will escape gradually as the Arctic permafrost melts but the scientists say the process could accelerate. As greenhouse gas levels soar, and soils warm, and plant roots tap down into the carbon stored there by centuries of ancient growth, they will release potent...